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M. G. KELLOGG. MULTIPLE SWITGHBOARD.

Patented Oct. 26,1897.

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MILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO TIIE KELLOGG S\VITCIIBOARD AND SUPPLY COMPANY, OF SAME PLACE.

MULTIPLE SWITCHBOARD.

SPECIFICATION forming part of Letters Patent No. 592,361, dated October 26, 1897.

Application led January l0, 1890. Serial No. 336,598. (No model.)

To @ZZ whom it, may concern:

Be it known that I, MILO G. KELLOGG, of Chicago, in the county of Cook and `State of Illinois, temporarily residing at Stuttgart, in the Empire of Germany, have invented certain new and useful Improvements in Multiple Switchboards for Telephone-Exchanges, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to a telephone-exchange system in which the subscribers lines are metallic-circuit lines, and the two sides or branches of each line are connected at the central oilice with the two contact-pieces of a loop-switch plug adapted to be inserted into any line-switch at the board where the plug is located and when inserted t0 connect the two lines together for conversation. Each line has a double or loop plug with a double cord attached and switches and apparatus connected with the circuit whereby an Operator to whom the line is given to answer its call may readily connect her telephone into the circuit for conversation, may readily connect her calling-generator into the circuit with a line wanted, may receive the clearingout signals, and perform the other usual operations of an exchange system. The double plugs and cords of the exchange are distributed among the different boards of the eX- change, and the special central-office apparatus, which belongs to any line, is conveniently located at the board where the cord and plug are located. Such a systemris called a sin gie-cord system.

My invention relates to a single-cord system for metallic-circuit lines.

The invention consists in a system of switches, apparatus, and connections for each line by which the operator may expeditiously connect her telephone to the circuit of the line to find out what is wanted, may connect the lines together for conversation, and may connecther calling-generator or her telephone into the circuit.

Figure l shows the central-office line apparatus and connections suilicient to illustrate my invention. Fig. 2 is a diagram of a subscribers-station apparatus to be used in connection with the system.

In the drawings like parts and apparatus are indicated by the same letters and igures of reference.

G in each case represents a ground connection.

I place as many switchboards in the central office as are found necessary or desirable in order to properly operate the exchange. On each board is a spring-jack or similar switch for each line. Each switch has a contactspring which normally connects with an insulated contact-piece. It has also a contactpiece insulated from the rest except `by the circuit connections. The switch is adapted to receive the loop-plugs, and when a plug is inserted it disconnects the spring from the contact-point and the two contact-pieces of the plug form connection with the spring and with said contact-piece, respectively.

In Fig. l, A and A' represent sections oi' two multiple switchboards to which the same lines are connected. g g represent the springs of the different switches, h 7L the contact-` points on which the springs normally bear, and j j the insulated contact-pieces of the switches. Z Z are the switch-holes. These 4holes are adapted to receive the switch-plugs of the lines located at their board and marked D D, and when a plug is inserted into a switch it disconnects the spring g from the contactpoint h and the tWo contact-pieces of the plug form connection with the spring'and with the piece j, respectively. j j are placed so that a test plug or device may be readily applied to them.

m m are the two contact-pieces of a switchplug, and they are connected to the circuit of the line to which their plug belongs, substantially as shown and as will be described. For each switch-plug is a switching device into which the plug is placed normally or when not in use for switching. This device has a contact-piece which is connected with the ground and with which one of the contact-pieces of t-he switch-plug is connected when the plug is inserted into the switching device. In these plug switching devices (marked C C) r is a metal contact-piece con- IOO ,other on the metal piece r, 5 being nearest piece fr, 4 being next to 5, 6 next to 4, and 7 farthest from piece r. Pieces 4 and 6 are spring-contacts connected near their top by a I rubber insulation-piece. Piece Gis an irregularly-shaped spring, which bears on the plug When the plug is inserted, but is insulated from the contact-piece of the plug, and is moved by the plug by an insulation-piece 6', which is placed on the surface against which the plug-handle bears, and has a projection which extends beyond piece 7, opposite the side thereof and in close proximity thereto, so as to come in contact with it when released from the pressure of the plug 011 its insertion, so as to make the switch connections I shall novvr describe. Vhen the plug is in the device, this piece 7 is pressed or wedged by the plug inte such a position that all the contactpieces are disconnected. Vhen the plug is withdrawn, the spring is released from the pressure of the plug and moves until it comes in contact with piece 7, and it carries or forces piece 4 into contact with piece 5.

The spring-jack switches of the lines are marked s s.

w and x are line-annunciators, one for each line shown.

P P are operators answering-switches, one

sul'ates the various parts of the answeringswitch. f f are two contact-springs.v l, 2,and 3 are contact-points located and insulated substantially as shown, and which form coninafter be described. The two springs are mounted parallel to each other and so that spring f is between point l and springfand close topoint l, and springf is between point 3 and spring f and close to point 3, while point 2 is between the two springs and close to springf'.

qis a sliding rod which passes through the frame cl. It terminates at one end in a butn. and o, respectively. This piece also movesv with the rod between the two springs, being carriedby the piece p.

The pieces Z q p and the rubber piece n o move together as one piece as the operator manipulates the button c. They may be called the com mutator-piece ofthe answerin g-'switch. The button eand the piece p furnish shoulders or stops for the commutatorpiece, which limit its inward and outward motions. When the commutator is pushed in until the outer stop is against or close to the standard of the frame, the two springsff rest on the piece p and are insulated from and unconnected withv the Contact points or pieces l, 2, and 3. When the commutator is pulled out to its central position, so that the springs ff rest on thecentral part o of the rubber piece, the spring f is in connection with the contact-piece l, and the spring f is in connection with the contact piece 3. l/Vhen the commutator is pulled out still farther, so that the inner shoulder is close to the standard of the fram'e, the spring f is in connection with the contact-piece 2, and the B is her calltact is then broken.

IO is the resistance-coil.

9 is the primary of the induction-coil, and S is the secondary of the coil. Both coils of the induction-coil should preferably have comparatively a large number of convolutions, and not merely the secondary coil, as

y is frequently the case in the construction of induction-coils.

B B are test-batteries.

T T are test plugs or devices, each attached by a flexible cord to its test-circuit and adapted to be brought for testing into connection with any of the contact-pieces jj at its board. neet-ions with said springs ff', as will here- There should be one key 7c, an operators telephone, an induction-coil, and a test-plug and cord for each operator.

For each line of the exchange, as before stated, there is a double-loop plug, a switching` device in which the plug is normally placed, an answering-switch, the spring-jack switches, one on each board, and the annunciator.

The connections of the line with its special apparatus and with the operators apparatus mentioned above are as follows: One side or branch of the line passes, successively, through Vthe pairs of contacts g h of the switches of the line on the several boards, passing in each case to the spring first. It then passes through the line-annunciator to contact-piece m of the loop-plug. The other side or branch of the line is connected with contact-piece m/ of the plug and is also con- She also has a 1 calling-generator and a test-battery.

IOO

nected with the contact pieces j j of the switches of the line.

One side of the operators calling-generator l5 and one side of her telephone t are connected to the contact-piece 3, and in the circuit-wire which connects the telephone and generator with piece 3 is placed the resistanee-coil 10. The other side of the generator is connected to the upper contact-point of the key k, and the lever of the key is connected to contactpiece l. The other side of the tele phone is connected through the secondary of the induction-coil and then passes to contactpiece 2. A branch wire or circuit passes from one side of the line-say to the'side connected with the contact-piecesjj--through the contactpoin'ts 5 and l of the plug switching device to one of the contact-springs-sayj4of the answering-switch. Another branch wire passes from the other side or branch of the line through the other contact-points G and 7 of the plug switching device to the other contact-spring f of the answering-switch.

The lower contactepoint of the key is con neetcd to that side of the operators telephone to which the secondary 8 of the inductioncoil is connected.

The operators test-plu g T, the test-battery B, and the primary 9 of her inductioncoil are connected together in a circuit which is grounded, as shown.

In the subscribeNs-station apparatus shown in Fig. 2, ll is the telephone-switch. Y12 is the callinggenerator. 13 is the signal-receiving bell, and lt is the subscribers telephone. One side of the subscribers circuit passes through the call-bell 13 to the switch 11 and thence to one side of the telephone. The other side of the circuit is connected with the op posite side of the telephone, with the calling- Y generator l2 between the telephone and line.

This side of the circuit is connected from a point between the generator and telephone .with the bottom contact of the telephoneswiich, so that the telephone is shunted when on it-s switch. The first-mentioned side of the line is connected from a point outside the call-bell with the top contact of the switch, so that the bell is shunted when the telephone is off its switch. These parts may be the usual forms of apparatus and may be eonnected as shown or in other ways, so as to produce the required result. The generator, however, is inoditied, as shown, according to a well-known term. lVhen it is not in operation, its armature is shunted through the frame of the generator and the subscribers line is open to the ground at his station. Vhilc it is being operated, the line is automatically grounded, with the armature-coil between said ground connection and the normal ground connect-ion of the line at the eent-ral oliice.

The operation of the system is as follows: l/Vhen a line is not in use, its plug rests in its switching' device, as described above, and the commntator of its answering-switch is pulled out and is substantially in the position in which it is shown in the drawings at board A. There is a complete circuit of one branch of the line through its switch contact-points and the annunciator, and thence through one ofthe strands ot the double cord to the contactpiece nl., and thence tothe ground through the switching device. Vhen a subscriber sends in a call on his generator, he temporarily grounds the line through the operation of the automatic device of the generator, with the armature-coil between said ground connection and the normal ofiice ground. A callin g-current passes over the line which operates the line-amiunciator. The operator then removes the plug from its normal position. Vhen she has done this, the ofiice ground of the line is removed and the pair of contactpoints 4 5 and the pair of contact-points 6 7 of the plug switching device are both closed. The two branches of the line are thereby placed on closed circuit with .the operators telephone in the circuit, and the operator iinds out by conversation what line is wanted. The circuit is from one branch of the line to contact 5, and thence through contact 4 and the circuit connection to spring f of the answeringswitch, thence through contact 3 and the circuit connection through the operators telephone to contact 2, thence through spring f and the circuit connection to contact 7, and thence through contact 6 and the circuit connection to the other side of the line. She then tests the line wanted, (by placing her test-plug on the contact-pieceg of the line,) and if she finds the line is not switched she places the loop-plug of the line on which the call came into the switch of the line wanted. By so doing she disconnects the contacts g h of the switch and connects the two sides of the line with the contact-pieces m fm of the plug, and this line also is disconnected from the office ground by the opening of the contacts g 7L. She then pushes in the commutator-picce of the answering-switch until it oceupies its inner position. (Shown at board A.) While the commntator-piece is passing over its central position Vwhere the spring f' rests on the piece O the operators generator is connected into the branch or bridge circuit which connects the two sides of thc line to which the answering-'switch belongs, and a calling-current passes through the circuit of both lines, the generator-current dividing or splitting into the two circuits. The circuit is from one branch of the line to contact 5, and thence through contact 4 and the circuit connection to spring f of the answeringswitch, thence through contact 3 and the circuit connection through the calling-generator to contact l thence through spring j" and the circuit connection to contact 7, and thence through contact G and the circuit connection to the other side of the line. Then the comlnutator-picce has reached the inner position, so that the springs ff rest on the rubber piece p, the springs are out of contact with IOO IIO

the contact-points Y1, 2, and 3, and the branch 0r bridge circuit is open at both points. The operators telephone and generator are then entirely disconnected from the circuit of the lines, and they are connected into an uninterrupted metallic circuit with the annunciator of the line in which the calloriginated in the circuit to receive a clearing-out signal.

When an operator desires to listen to vdetermine whether the subscribers are through conversation, she presses down the lever of the key 7c, and while it is in that position draws the commutator-piece of the answeringswitch out, so that it occupies the central position, with the springs ff' resting on the part o. The branch or bridge circuit is then closed by the connections between f and 3 and betweenf and-2 and the circuit connections, as heretofore traced, and the operators telephone is inthe bridge-circuit and she will hear the conversation without interrupting it. I prefer to have a resistance-coil equal to at least the resistance otany line 'of the eX- change placed in circuit with the telephone in the-branch or bridge circuit, so as not to shunt an undue amount of the telephone-current into the bridge-circuit which contains the telephone when she connects her telephone to the circuit,.as-described. This resistance-coil. is marked 10. It is placed in the circuit-wire whichA connects the contactpoint 3 withthe operators-telephone and generator. p

When the operator desires to clear out a connection, she takes the loop-plug Jfrom the switch andk places it in its switching device.

By. so doing the lines are disconnected from,

each other, their normal ground connections are again established, and the pairs of contact-points 4:, 5 and 6 7'are again opened. The operator then places the answering-switch in its normal position, where the contact-springs ff' resten the rubber piece n, and the apparatus is inpositiontoreceive a new call on the line. When a new callis receivedron the annunciator, she connects her telephone to the .circuit by the mere act of, withdrawing fore described.

When. an operator tests a line, as heretofore mentioned, and the lineis not switched, a complete circuit is established from the ground connection of the test-battery to the normal ground connection of the line, and a battery-currentpasses over the circuit. This circuit is from the ground through the primary 9 ofl the ind uction-coil and the test-battery B.' to contact-piecej` of the switch, thence through the circuit of the line by Way of the subscribers station, thence through the pairs of contacts g h of the line-switches, and thence through the connection between piece m of the switch-plug and the metal piece r of the switching device to the ground. This operates through the operators induction-coil to send an induction-current through the operators telephone (which is then on closed circuit with the-line in which the call originated) and she will hear a click in the telephone and know that theline is free to be switched to. Il", however, the line tested is switched at any board, it is disconnected from the ground and n there will be no current established and'therefore no click in the telephone. If the line is It" it is switched by the use of its switch-plug, it is disconnected from the ground by the opening of the contact between piece fm of the plug and piece r,

in which the plug is normally placed.

Each operators special apparatus, which includes her telephone, key, resistance-coil, induction-coil, testplug, calling-generator, and battery, are connected to the answeringswitch of each line assigned to her to answer, substantially as shown and vdescribed for the lines shown in the drawings.

I prefer to have the key 7o actuated by a cam-lever, as shown in the drawings, or to have some other mechanism by which the contact-spring of the key may be placed in one or the other of the two positions and left there without the continued manipulation of the operator. By this means an operator may place the key in position where her telephone is connected to the lever, leave it there,A and be free to operate one after another of her answering-switches, so as to listen to determine whether the subscribers connected together are through conversation.

By the organization as described the operator is enabled to answer a subscriber, make his connection with another line, and call on the line with a minimum of operations and work. These operations are merely to take his plug from its normal position, piace her test-plug on the test-piece of the line wanted, vplace the plug in the switch of the line wanted, and push the commu tator-piece into its inner position. y

I claim as my invention and desire to secure by Letters Patenttheplug from itsswitching device, as heretol. In a telephone-exchange system, a metallic-circuit line, the two sides or branches of which are normally open to each other at the central office; a switch-plug for the line, a switching device for the plug into which the plug is normally inserted, two pairs of contact-points in said switching device insulated from each other (except by the circuit connections), the two con tact-points of each pair being in contact while the plug is out of the switching device and out of contact-while the plug is inserted inthe device, in combination with a bridge or connecting wire for said line the two ends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contactpoints, and an answering-switch for the line with contact-points by which the operator may at will loop her telephone into the circuit of said bridge-wire between said pairs of IOO IIO

contact-points of the switching device or disconnect her telephone from the bridge-wire and leave said wire open at the answeringswitch, substantially as set forth.

In a telephone-exchange system, a metallic-circuit line, a switch-plug for the line, a switching device for the line into which the plug is normally inserted, two pairs of contact-points in said switching device insulated from cach other (except by the circuit connections), the two contact-pieces of each pair being in contact while the plug is ont of the switching device and out of contact while the plug is inserted into the device, in combination with a bridge or connecting wire for said line the two ends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contact-points, and an answering-switch for the line with contactpeints by which the operator may at will either loop her telephone into the circuit ef said bridge-wire between said pairs of contact-points of the switching device or may loop her generator into said bridge-wire between said pairs of points, or may leave the bridge-wire open at the answering-switch with neither her telephone nor generator connected to it, substantially as set forth.

In a telephone-exchange system, a inetallic-circuit line, a switch-plug for the line, a switching device for the plug in which the plug is normally inserted, two pairs of contact-points in said switching device insulated from each other (except by the circuit connections), the two contact-points of each pair being in contact while the plug is out et' the device and out of contact while the plug is in the device, in combination with a bridge or connecting wire for said line the two ends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contact-points,and an answeringswitch for the line with contact-points and connections and a cominutator-piece adapted to be placed in three positions successively at the will of the opera-tor, in the first position of which her telephone is looped into the circuit of said bridge-wire between said pairs of contact-points of the switching device, in the nent position of which the calling-generator is looped into the circuit of the bridge-wire between said pairs of points and in the last position of which said bridge-wire is left open at the answering-switch with neither the telcphone nor the generator connected to it, substantially as set fort-h.

et. In a telephoneexchange system, a metallic-circuit line, a switch-plug for the line, a switching device for the plug into which the plug is normally inserted, two pairs of contactpoints in said switching device insulated from each other (except by the circuit connections), the two contact-points of each pair being in contact while the plug is out of t-he de vice and out of contact while the plug is in the device, in combination with a bridge or connecting wire forsaid line the two ends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contact-points, an answering switch for the line with contact-points and connections and a commutator-piece adapted to be placed in three positions successively,at the will of the operator, in the first position of which her telephone is looped into the circuit of said bridge-wire between said pairs of contact-poin ts of the switching device, in the next position et' which the callinggeuerator is normally looped into the circuit of the bridge-wire between said pairs of points and in the last position of which said bridge-wire is left open at the answeringswitch with neither the telephone nor the generator conneeted to it, and a key or switch with contactpoints by which when the coininutator is in said second position the circuit through the generator may be broken, substantially as set forth.

5. In a telephone-exchange system, a mc tallic-circuit line, a switch-plug for the line, a switching device for the plug into which the plug is normally inserted, two pairs of contact-points in said switching device insulated from each other (except by the circuit connections), the two contact-points of each pair being in contact while the plug is out of the device and out of contact while the plug is in the device, in combination with a bridge or connecting wire for said line the two ends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contactpoints, an answering-switch for the line with contact-points and connections and a commutator-piece adapted to be placed in three positions successively, at the will of the operator, in the first position of which her telephone is looped into the circuit of said bridge-wire between said pairs of contact-points of the switching device, in the next position of which the calling-generator is normally looped into the circuit of the bridge-wire between said pairs of points and in the last position of which said bridge-wire is left open at the answeringswitch with neither the telephone nor the generator connected to it, and a key or switch with contact-points by which when the commutator is in said second position the circuit through the gen erator may be broken and the circuit established through the telephone, substantially as set forth.

6. In a telephone-exchange system, a 1netallic-circnit line, the two sides or branches of which are normally open to each other at the central oflice, a loop-switch plug for the line in the two contactpieces of which terminate the two sides or branches of the line, said plug being adapted to be inserted into the switch of any other metallic-circuit line at its board and when inserted to connect the contact-pieces of the switch with the two sides or branches of the line, a switching device for the plug into which the plug is normally in- IOO serted, two1 pairs of contact-points in said switching device insulated from each other (except by the circuit connections), the two contact-points of each pair being in contact while the plug is out of the switching device and out of contact while the plug is inserted in the device, in combination with a bridge or connecting wire for said line, the two ends of which are 'connected to the two sides or branches of the line respectively and in which are said two pairs of contact-points, and an answering-switch for the line with contact-` points by which the operator may at will loop her telephone into the circuit of said bridgewirebetween said pairs of contact-points of the switching device or disconnect her telephone from the bridge-wire and leave said wire open at the answering-switch, substantially as set forth.

7. In a telephone-exchange system, a inetallic-circuit line, a loopswitch plug for the line in the two contact-pieces of which terminate the two sides or branches of the line, said plug being adapted to be inserted into the switch of any other metallic-circuit line at its board and when inserted to connect the con tact-pieces of the switch with the two sid es or branches of the line, a switching device for the line into which the plug is normally inserted, two pairs of contact-points in said switching device insulated from each other (except by the circuit connections), the ltwo contact-pieces of each pair being in contact while the plug is out of theA switching device and out of contact while the plug is inserted into the device, in combination with a bridge or connecting wire for said line the two ends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contact-points, and an answering switch for the line with contact-points by which the operator may at will either loop her telephone into the circuit of said bridge-wire between said pairs of contact-points of the switching device or may loop her generator into said bridge-wire between said pairs of points, or may leave the bridge-wire open at the answering-switch with neither her telephone or generator connect-ed to it, substantially as set forth.

8. In a telephone-exchange system, a metallic-circuit line, a loop-switch plug for the line in the two contact-pieces of which terminate the two sides or branches of theline, said plug being adapted to be insert-ed into the switch of any other metallic-circuit line lat its board and when inserted to connect the contact-pieces of the switch with the two sides or branches of the line, a switching device for the plug into which the plug is normally inserted, two pairs of contact-points in said switching device insulated from each other (except by the circuit connections), the two contact-points of each pair being in contact while the plug is out of the device and out of contact while the plug is inthe device, in combination vwith a bridge or connecting wire for said line the two lends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contact-points, and an answering-switch for the line with contact-points and connections and a commutatonpiece adapted to be placed in three positions successively at the will of the operator, in the iirst position of which her telephone is looped into the circuit of said bridge-wire between said pairs of contact-points .of the switching device, in the next position of which the calling-generator is looped into the circuit of the bridge-wire between said pairs of points and in the last position of which said bridgewire is left open at the answering-switch with neither the telephone nor the generator connected to it, substantially as set forth.

9. In a telephone-exchange system, a inetallic-circuit line, a loop-switch plug for the line in the two contact-pieces of which terminate the two sides or branches of the line, said plug being adapted to be inserted into the switch of any other metallic-circuit line at its board and when inserted to connect the contact-pieces of the switch with the two sides or branches of the line, a switching device for the plug into which the plug is normally inserted, two pairs of contact-points in said switching device insulated from each other (except by the circuit connections), the

two contact-points of each pair being in contact while the plug is out of the device and out of contact while the plug is in the device, in combination with a bridge or connecting wire for said line the two ends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contact-points, an answering-switch for the line with contact-points and connections and a commutator-piece adapted to be placed in three positions successively, at the will of the operator, in the iirst position of which her telephone is looped into the circuit of said bridge-wire between said pairs of contact-points of the switching device, in the next position of which the calling-generator is normally looped into the circuit of the bridge-wire between said pairs of pointsand in the last position of which said bridge-wire is left open at the answering-switch with neither the telephone nor the generator connected to it, and a key or switch with contact-points by which when the commutator is in said second position the circuit through the generator may be broken, substantially as set forth.

Al0. In a telephone-exchange system, a metallic-circuit line, a loop-switch plug for the line in the two contact-pieces of which terminate the two sides or branches of the line, said plug being adapted to be inserted into the switch of any other metallic-circuit lineY IOO IIO

592,361 g l 'r mally inserted, two pairs of contact-points in said switching device insulated from each other (except bythe circuit connections), the two contact-points of each pair being in contact while the plug is out of the device and out of contact while the plug is in the device, in combination with a bridge or connecting wire for said line the two ends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contact-points, an answering-switch for the line with contact-points and connections and a commutator-piece adapted to be placed in three positions successively, at the will of the operator, in the first position of which her telephone is looped into the circuit of said bridge-wire between said pairs of contact-points of the switching device, in the next position of which the calling-generator is normally looped into the circuit of the bridge-wire between said pairs of points and in the last position of which said bridge-wire is left open at the answering-switch with neither the telephone nor the generator connected to it and a key or switch with contactpoints by which when the cominutator is in said second position the circuit through the generator may be broken and the circuit established through the telephone, substantially as set forth.

l1. In a telephone-exchange system, a plug switching device for a metallic-circuit line, adapted to receive a loop-switch plug for the line when the plug is not in use, the two contact-pieces of the plug being connected through fiexible conductors to the two sides or branches of the line, respectively, said plug switching device having two pairs of contact-points which are open while the plug is in the device but automatically closed on the withdrawal of the plug, two contact-points, one of each pair, being connected to the two sides of the line, respectively, two of said contacts, one of each pair being springs moved by the plug on its insertion to open the two pairs of points and the two other points being immovable or stationary on the withdrawal or insertion of the plug, in combination with an answering-switch for said line, having two pairs of contact-points normally in contact but opened at the will of the operator, two of such contact-points, one of each pair being connected to the two other contact-points, respectively, of the plug switching device, and the two other contact-points of the operators switching device being connected to the two sides, respectively, of the operators telephone, substantially as set fort-h.

l2. In a telephone-exchange system, a plug switching device for a metallic-circuit line, adapted to receive a loop-switch plug for the line when the plug is not in use for switching, the two contact-pieces of the plug being connected, through iiexible conductors, to the two sides or branches, respectively, of the line, said plug switching device having two pairs of contact-points which are open when the plug is in the device but are automatically closed on the withdrawal of the plug, two contact-points, one of each pair, being connected to the two'sidcs or branches of the line, in combination with an answering-switch for said line, having two pairs of contact-points, two contact-points of which are connected to the two other contact-points of the plug switching device, one of the other peints being connected to one side of the operators telephone and also to one side of her calling-generator and the other point connected to the other side of the telephone, and a fifth point normally out of contact with the other points and connected to the other side of the generator, and a commutator-piece adapted at the will of the operator to be placed in three positions, when in its normal position the two pairs of contact-points of the answering-switch being in contact, when in its next position the pair to which are connected one side of the telephone and generator remaining in contact and the other pair being separated and that one which is connected with the line brought into contact with said iifth point, and when in the third position all the contact-points of the answering-switch being out of contact, substantially as set forth.

13. In a telephone-exchange system, a metallic-circuit line, a loop-switch plug for the line, to the two contact-pieces of which, respectively, are connected, through flexible conductors, the two sides or branches of the line, a plug switching device into which the plug is placed when not in use, having pairs of contacts therein and connections by which the operators telephone is bridged across the two sides of the line when the plug is withdrawn from said device, in combination with an answering-switch having pairs of contacts and a commutator-piece therein, and connections by which thc operator may at will disconnect said bridge connection through the telephone and connect her calling-generator in a bridge across the two sides of the line and may disconnect both telephone and generator from the line, substantially as set forth.

14:. In an answering-switch for a telephoneline, a contact-spring and two contact-points, one point on each side of said spring and another contact-spring and a contact-point placed near the spring in combination with a commutator-piece adapted to be moved between the springs and, on which they press, said commutator-picce having on one side three commutator-s ur'faces in different planes on which said first-mentioned spring alternately presses and on another side two commutator-surfaces only in dierent planes on which said second-mentioned spring alter- Vnately presses, substantially as set forth.

15. In an answering-switch for atelephoneline, a contact-spring and two contact-points, one point on each side of said spring and another contact-spring and a contact-point placed near the spring, in combination with a commutator-piece adapted to be moved be- IOO IIO

tween the springs and on which they press, said commutator-piece having on one side three commutator-surfaces in different planes against which said first-mentioned spring alternately presses, the iirst surface being nearest the axis of said piece in its line of motion, the second surface being' farthest from said axis and the third surface being in a plane between the two other surfaces, and having on another side two comm utator-surfaces against which said second-mentioned spring alternately presses, the irst commutator-surface being farther than the other from the axis of the commutator-piece in its line of motion, substantially as set forth.

16. In atelephone-exchange system, a metallic-circuit line, the two sides or branches of which are normally open to each other at the central office, a switch-plug for the line, a switching device for the plug into which the plug is normally inserted, a pair of contacts, one connected with the line and the other with the ground, normally closed butopen on the withdrawal of the plug from the switching. device, two pairs of contact-points in said switching device insulated from each other (except by the circuit connections) the two contact-points of each pair being in contact while the plug is out of the switching device and out of contact while the plug is inserted in the device, in combination with a bridge or connecting wire for said line the two ends of which are connected to the two sides or branches of the line respectively and in which are said two pairs of contact-points, and an answering-switch for the line with contact-points by which the operator may at will loop her telephone into the circuit of said bridge-wire between saidpairs of contactpoints of the switching device or disconnect her telephone from the bridge-wire and leave said wire open lat the answering-switch, substantially as set forth.

17. In a telephone-exchange system, a metallic-circuit line, the two sides or branches of which are normally open to each other at the central office, a loop-switch plug for the line in the two contact-pieces of which terminate the two sides or branches of the line, said plug being adapted to be inserted into the switch of the other metallic-circuit line at its board and when inserted to connect the contact-pieces of the switch with the two sides or branches of the line, a switching device for the plug into which the plug is normally inserted, a pair of contacts, one connected with the line and the other with the ground, normally closed but open on the withdrawal of the plug from the switching device, two pairs of contact-points in said switching device insulated from each other (except by the circuit connections), the two contactpoints of each pair being in contact while the plug is out of the switching deviceand out of contact while lthe plug is inserted in the device, in combination with a bridge or connecting wire for said line, the two ends of which are connected. to the two sides or branches of the line respectively and in which are said two pairs ot' contact-points, and an answering-switch for the line with contactpoints by which the operator may at will loop her telephone into the circuit of said bridgewire between saidl pairs of contact-points of the switching device or disconnect her telephone from the bridge-wire and leave said wire open at the answering-switch, substantially as set forth.

le. In a telephone-exchange system, a plug switching device for a metallic-circuit line, adapted to receive a loop-switch plug for the line when the plug is not in use, the two contact-pieces of the plug being connected through iiexible conductors to the two sides or branches of the line, respectively, said lu T switching device containing a grounded- Z7 n C v contact-piece with which a contact-piece of the plug connected with the line is normally in contact and also containing two pairs of contact-points which areopen while the plug is in the device but automatically closed on the withdrawal of the plug, two contactpoints, one of each pair being connected to the two sides of the line, in combination with an operators switching device for said line, having two pairs of contact-points normally in contact but opened at the will of the operator, two of such contact-points, one of each pair, being connected to the two other contact-points, respectively, of the plug'switching device, and the two other contact-points of the operators switching device being connected to the two sides, respectively, of the operators telephone, substantially as set forth.

19. In a telephone-exchange system, a metallic-circuit line, a loop-switch plug for the line to the two contact-pieces of which, respectively, are connected the two sides or branches of the line, a plug switching device into which the plug is placed normally or when not in use and a bridge circuit or connection for said line containing the operators telephone said circuit being normally open but automatically closed by the plug switching device on the withdrawal of the plug from its normal position, in combination with a calling-generator and a commutator-piece moved in one direction at the will of the operator to occupy three positions, in one of which her telephone is in said bridge circuit or connection, in another of which the generator is connected with and the telephone disconnected from the line and in another of which neither the telephone nor the generator is connected with the line.

In witness whereof I hereunto subscribe my name this 20th day of December, 1889.

MILO G. KELL GG, lVitnesses:

EMIL ABENHEIM, MAnGARnrI-IA RIEHL.

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